| Title: |
Molecular line emission in NGC 4945, imaged with ALMA |
| Authors: |
Henkel, C; Muehle, S; Bendo, G; Jozsa, GIG; Gong, Y; Viti, S; Aalto, S; Combes, F; Garcia-Burillo, S; Hunt, LK; Mangum, J; Martin, S; Muller, S; Ott, J; van der Werf, P; Malawi, AA; Ismail, H; Alkhuja, E; Asiri, HM; Aladro, R; Alves, F; Ao, Y; Baan, WA; Costagliola, F; Fuller, G; Greene, J; Impellizzeri, CMV; Kamali, F; Klessen, RS; Mauersberger, R; Tang, XD; Tristram, K; Wang, M; Zhang, JS |
| Source: |
Astronomy & Astrophysics , 615 , Article A155. (2018) |
| Publisher Information: |
EDP SCIENCES S A |
| Publication Year: |
2018 |
| Collection: |
University College London: UCL Discovery |
| Subject Terms: |
Science & Technology; Physical Sciences; Astronomy & Astrophysics; galaxies: starburst; galaxies: structure; galaxies: ISM; nuclear reactions; nucleosynthesis; abundances galaxies; individual: NGC4945; radio lines: ISM; DENSE GAS; NEARBY GALAXIES; NUCLEAR STARBURST; ACTIVE NUCLEUS; MASER EMISSION; CHEMICAL EVOLUTION; VLA OBSERVATIONS; GALACTIC NUCLEI; NGC-4945; CLOUDS |
| Description: |
NGC 4945 is one of the nearest (D ≈ 3.8 Mpc; 1″ ≈ 19 pc) starburst galaxies. To investigate the structure, dynamics, and composition of the dense nuclear gas of this galaxy, ALMA band 3 (λ ≈ 3−4 mm) observations were carried out with ≈2″ resolution. Three HCN and two HCO+ isotopologues, CS, C3H2, SiO, HCO, and CH3C2H were measured. Spectral line imaging demonstrates the presence of a rotating nuclear disk of projected size 10″ × 2″ reaching out to a galactocentric radius of r ≈ 100 pc with position angle PA = 45° ± 2°, inclination i = 75° ± 2° and an unresolved bright central core of size ≲2″. The continuum source, representing mostly free-free radiation from star forming regions, is more compact than the nuclear disk by a linear factor of two but shows the same position angle and is centered 0.′′39 ± 0.′′14 northeast of the nuclear accretion disk defined by H2O maser emission. Near the systemic velocity but outside the nuclear disk, both HCN J = 1 → 0 and CS J = 2 → 1 delineate molecular arms of length ≳15″ (≳285 pc) on opposite sides of the dynamical center. These are connected by a (deprojected) ≈ 0.6 kpc sized molecular bridge, likely a dense gaseous bar seen almost ends-on, shifting gas from the front and back side into the nuclear disk. Modeling this nuclear disk located farther inside (r ≲100 pc) with tilted rings provides a good fit by inferring a coplanar outflow reaching a characteristic deprojected velocity of ≈50 km s−1. All our molecular lines, with the notable exception of CH3 C2H, show significant absorption near the systemic velocity (≈571 km s−1), within the range ≈500–660 km s−1. Apparently, only molecular transitions with low critical H2 density (ncrit ≲ 104 cm−3) do not show absorption. The velocity field of the nuclear disk, derived from CH3 C2H, provides evidence for rigid rotation in the inner few arcseconds and a dynamical mass of Mtot = (2.1 ± 0.2) × 108 M⊙ inside a galactocentric radius of 2.′′45 (≈45 pc), with a significantly flattened rotation curve farther out. Velocity integrated ... |
| Document Type: |
article in journal/newspaper |
| File Description: |
text |
| Language: |
English |
| Relation: |
https://discovery.ucl.ac.uk/id/eprint/10056178/1/Henkel_Molecular.pdf; https://discovery.ucl.ac.uk/id/eprint/10056178/ |
| Availability: |
https://discovery.ucl.ac.uk/id/eprint/10056178/1/Henkel_Molecular.pdf; https://discovery.ucl.ac.uk/id/eprint/10056178/ |
| Rights: |
open |
| Accession Number: |
edsbas.F30E13C5 |
| Database: |
BASE |